[ELI5] Why do LEDs in cars flicker? Aren’t they powered by DC?

Question

I understand why we see them flicker in videos, but why do LEDs flicker at all when they’re powered with DC?

In: 2

Answer 1

Your car uses an alternator to generate AC power, because an alternator is lighter and cheaper than an equivalent DC generator. This AC power is then converted into DC using a rectifier. The rectification circuitry used in most cars is not very high quality, so the DC power fluctuates a lot around the desired (~14v) level. Powering LEDs off of this poor quality DC power will make them flicker, at least a little bit. Depending on the quality of the rectification circuit, and the LED driver circuit, the flicker may be more or less noticeable.